For optically interconnecting a plurality of optical fibers to a plurality of optical fibers, or for optically interconnecting a plurality of optical fibers to one or a plurality of optical parts, desirably, each of optical fibers to be connected are highly accurately fixed in advance. For example, in an optical fiber tape formed by arranging a predetermined number of single-mode optical fibers side by side, each optical fiber has a core diameter of about 10 .mu.m, and these optical fibers are arranged at a pitch of approximately 126 to 250 .mu.m. It is therefore desired for optical interconnection to arrange end portions of these optical fibers in a locational accuracy of within .+-.0.5 .mu.m.
For the optical interconnection of a plurality of optical fibers, there is therefore used in many cases a member which fixes end portions of these optical fibers highly accurately (the above member will be referred to as "optical fiber fixing member" hereinafter), such as an optical fiber guide block. The optical fiber guide block is a thin-sheet block having an upper surface (one surface) on which a predetermined number of optical fiber fitting portion(s) for fixing end portion(s) of optical fiber(s) is/are formed. The locational accuracy of optical fibers fixed in the optical fiber guide block is dependent upon the work accuracy of the optical fiber fitting portion(s) formed on the optical fiber guide block.
The above optical fiber guide block is largely classified into an optical fiber guide block having the above optical fiber fitting portion(s) alone and an optical fiber guide block having (i) an optical fiber fixing part having an upper surface on which optical fiber fitting portion(s) is/are formed and (ii) a lower-staged part whose upper surface is formed in a position lower than the above optical fiber fitting portion(s). The lower-staged part of the latter type is used as a base for fixing optical fibers protected with coating portions together with the coating portions.
In an optical fiber guide block of any type, optical fiber fitting portion(s) is/are conventionally formed by (i) an etching method when a silicon substrate is used as a raw material or by (ii) a grinding method when glass such as quartz glass or Pyrex glass is used as a raw material. In recent years, however, it has been actively attempted to produce an optical fiber guide block by a mold shaping method (press-molding method). The mold shaping method is promising as a method which can provide an optical fiber guide block having high accuracy in optical fiber fitting portion(s) and high accuracy in appearance and having stability in these properties of accuracy, with high producibility at a low cost.
For producing a desired mold-shaped article by a mold shaping method, parameters such as the substructure of a shaping mold and shaping conditions are naturally essential, and the geometric form and dimensions of a shapable material (preform) also affect the work accuracy and the appearance form accuracy of a mold-shaped article. It is therefore essential to determine a proper form and dimensions of the preform for improving the yield of non-defective products produced by the mold shaping.
For example, in the mold shaping method described in JP-B-61-32263, a preform is formed so as to have a form similar to the form of a lens as an end product, and a glass lens is fabricated by properly selecting t.sub.0, P and .mu. depending upon C=t.sub.0 P/.mu. in which C is a value dependent upon a difference between the form of a shaping mold (cavity form) and the form of a preform (C decreases with a decrease in the above difference), t.sub.0 is a time period necessary for bringing the form of a preform into conformity with the form of a shaping mold (cavity form) during press-shaping (mold shaping), P is a hydrostatic pressure inside glass (preform) when the glass is sufficiently pressed during press-shaping and .mu. is a viscosity of the glass during the press-shaping (mold shaping).
Since, however, an optical fiber guide block is a thin-sheet-like block (its maximum thickness is, for example, approximately 1.0 to 1.5 mm), the flow of a shapable material does not easily occur during mold shaping. When the optical fiber guide block as an end product is a type having an optical fiber fixing part and a lower-staged part, it is required to form a level difference between the optical fiber fixing part and the lower-staged part. The formation of the above level difference makes it very difficult to cause the flow of a shapable material from a small-thickness portion to a large-thickness portion through the above level-difference portion, or in a direction counter thereto, during mold shaping. Further, when the mold shaping is carried out to obtain an optical fiber guide block, it is required to attain the two purposes, pattern transfer (formation of optical fiber fitting portion(s)) and formation of an appearance, by one cycle of mold shaping.
It is therefore more difficult to produce optical fiber guide blocks of the type having an optical fiber fixing part and a lower-staged part at high yields of non-defective products by mold shaping than to produce lenses at a high yields of non-defective products by mold shaping.
If the viscosity of a shapable material during mold shaping is decreased to less than 10.sup.7.6 poise, it is possible to cause the sufficient flow of the shapable material even when an optical fiber guide block having an optical fiber fixing part and a lower-staged part is produced. However, when the viscosity of a shapable material is so decreased, the following problems occurs. That is, the problems are that (i) the accuracy of transfer of a pattern for optical fiber fitting portion(s) decreases, and that (ii) the flow of a shapable material is liable to become non-uniform so that the shapable material is liable to flow out through gaps (clearances) of a shaping mold to cause burrs on corners and edges of a mold-shaped article (optical fiber guide block).
An optical fiber guide block of a type having an optical fiber fixing part and a lower-staged part can be also obtained by a method in which the optical fiber fixing part alone is formed during mold shaping and then the lower-staged part is formed by grinding work. However, this method requires an additional step, which results in an increase in a production cost and a decrease in producibility.